[Unit]
Description=BubbleCam: seed system clock from DS3231 hardware RTC
# Must run before anything time-dependent (sensors, lumen dusk/dawn calc,
# watchdog staleness checks) -- without this, a cold boot with no network
# would come up with a garbage system clock (no NTP available in the field).
DefaultDependencies=no
After=dev-rtc0.device
Before=basic.target
# Deliberately NOT Wants=dev-rtc0.device: that makes systemd *wait* for the
# device unit, and since this unit is Before=basic.target, the entire boot
# (NetworkManager included) queues behind it -- observed as an ~80s stall
# before the network came up. The bounded ExecStartPre poll below gives the
# RTC a fair chance to appear without ever holding the boot hostage.
JobTimeoutSec=30
# This is a boot-time oneshot with no running process -- there is nothing
# to stop, and a stop job on a Before=basic.target unit stalls until it
# times out, which silently takes the rest of a `systemctl stop
# 'bubblecam-*'` transaction down with it (observed: the e-paper service
# stayed running, still holding the camera).
RefuseManualStop=yes

[Service]
Type=oneshot
# Poll for the device rather than depending on it: up to ~10s, then give up
# and continue booting regardless.
ExecStartPre=/bin/sh -c 'for i in $(seq 1 20); do [ -e /dev/rtc0 ] && exit 0; sleep 0.5; done; exit 0'
# -s = set the system clock from the hardware RTC. Requires the kernel
# rtc-ds1307 driver to be bound via config.txt's `dtoverlay=i2c-rtc,ds3231`
# (see boot/firmware/config.txt.bubblecam-append) so /dev/rtc0 exists.
# Leading "-": a missing/failed RTC must not fail the unit or stall boot --
# the system clock then just falls back to whatever the OS has.
ExecStart=-/sbin/hwclock -s
TimeoutStartSec=20
RemainAfterExit=yes

[Install]
WantedBy=basic.target